Systems and methods for reliable relative navigation and autonomous following between unmanned aerial vehicle and a target object

ABSTRACT

A method for navigating an airborne device relative to a target comprises detecting, at an optical detector on the airborne device, an optical signal generated by one or more LEDs on the target. The method also comprises comparing, by a processor on the airborne device, the detected optical signal with a previously-detected optical signal. The method further comprises determining, by the processor based on the comparison, a change in location of at least one of the airborne device or the target. The method also comprises adjusting a position of the airborne device based on the determined change in location. The method also comprises predicting, by the processor, a movement of the target based on information indicative of at least one of a position, a rotation, an orientation, an acceleration, a velocity, or an altitude of the target, wherein the position of the airborne device is adjusted based on the predicted movement of the target. The method also comprises detecting an obstacle in a flight path associated with the airborne device and adjusting a position of the airborne device is further based, at least in part, on detected obstacle information.

TECHNICAL FIELD

The present disclosure relates generally to unmanned aerial vehiclesand, more particularly, to systems and methods for effectively andaccurately navigating an unmanned aerial vehicle relative to astationary or mobile target.

BACKGROUND

In manner very similar to how smartphones revolutionized personalcomputing, unmanned aerial vehicles (“UAVs”) are poised to change ourcivilian society in ways that have yet to be imagined. While it is tooearly to predict all of the areas of life in which UAVs will have animpact impact, it appears all but certain that their widespread use isimminent.

One of the key technologies enabling autonomous (as opposed to piloted)use of UAVs is positioning and control. Conventionally, UAV designershave put emphasis on absolute positioning (the specific location orposition of the UAV in a coordinate space), since it has generally beenthought of as being instrumental to the success of the mid- tohigh-altitude intelligence, surveillance, and reconnaissance (“ISR”)missions where UAVs have typically been used by the military (theprimary user of UAVs to date). With the proliferation of low-flyingportable UAVs (e.g. multi-rotors), however, reliable relativepositioning, independent of GPS, is crucial. This will enable UAVs tosafely operate in close proximity to and relative to other (mobile)humans and machines, for both military and civilian applications.

The past five years have seen an explosion in consumer “drones”, withsome as inexpensive as $300. As this technology matures (e.g., in termsof endurance for VTOL multi-copters), prices continue to decrease, andthe regulatory environment opens their wider use, various types of UAVswill find numerous consumer, commercial, and governmental applications.Indeed, the use of personal UAVs—those that can be operated by a singleuser and function with a level of autonomy that enables their user tocarry on his various tasks without having to dedicate much attention tothe vehicle operation—are expected to increase dramatically in thecoming years. Personal UAVs can be thought of as physical extensions ofthe user, and as such tightly follow their user motion—just as arms andlegs move with the rest of one's body.

To ensure their widespread adoption, personal UAVs generally cannotrequire their user to become skilled remote control pilots. In addition,they should operate as autonomously as possible, in order to free theuser to focus on the specific activity, instead of worrying aboutoperating the UAV.

Before such personal UAVs can become a reality, therefore, they shouldgenerally be able to reliably and accurately follow their userregardless of the user's dynamics and regardless of the environment(GPS/no GPS, indoor/outdoor, open/urban,line-of-sight/non-line-of-sight) and of obstacles. The user can be aperson (walking, running, biking, skiing, racing, etc.), an animal(military/search-and-rescue dog), another vehicle (a car, a truck, apiloted UAV, an unmanned UAV), or a stationary reference (landing pad ornavigation beacon).

UAV positioning and control technologies have so far focused onperforming these tasks in the absolute frame, i.e., with respect toglobal Earth coordinates. Exceptions do exist, especially for launch andrecovery operations, but in such cases the technology used is either notsuitable to mobile applications (e.g. landing radar) or the requirementit places on GPS availability makes it unsuitable to most urban andindoor applications. Developing such technology for personal UAVsindependently of the availability of GPS will be the focus of our work.

The presently disclosed relative navigation system addresses many of theproblems and issues set forth above, thereby enabling UAVs to beoperated by personnel without piloting skill. As such, the presentlydisclosed system allows operators to simply designate where the UAV isto be positioned at all times by either embedding target deviceelectronics in the object of interest, or by designating the desiredlocation using a collimated light source. In addition, the presentlydisclosed system enables the UAV to automatically detect and avoidobstacles located within its path. Accordingly, the presently disclosedsystems and methods for effectively and accurately navigating anunmanned aerial vehicle relative to a mobile target are directed toovercoming one or more of the problems set forth above and/or otherproblems in the art.

SUMMARY

A system providing reliable, high-accuracy relative navigation for smallUAVs is desirable. Systems and methods associated with thepresently-disclosed embodiments enable small UAVs to autonomously followmobile users at close range, regardless of the operating andenvironmental conditions (urban, mountainous, day/night/weather, GPS(un-)availability, LOS/NLOS). Systems and methods consistent with thedisclosed embodiments take advantage of the mobility of the UAV,multiple sensors, and advanced fusion and control algorithms toaccurately resolve and control the position of the UAV relative to theuser. Additionally, the system leverages its collaborative relationshipwith the user to provide a reliable approach to obstacle avoidance thatis suitable for small UAVs. This system is platform-agnostic and will besuitable to most small UAS currently available.

According to one embodiment, the UAV system generally consists of aso-called Airborne Device (AD), located onboard the UAV, which containsa variety of sensors and processes their information in our navigationsoftware. The AD can also leverage information from an optional targetdevice, containing a suite of sensors and a data link to the AD. Thetarget device is not required for the AD to provide a full relativenavigation solution. However including the target device makes thesystem more robust to user motion and to other environmentaldisturbances, virtually guaranteeing the accuracy of the relativenavigation solution regardless of the operating scenario.

The presently disclosed system provides the following key attributes toany small UAV: (A) autonomy: Requires little to no user input, so theuser can focus on his task (“launch and forget”); and (B)availability: 1) Can be deployed and recovered automatically anywhere,even from moving vehicles, and 2) Functions in harsh operationalenvironments (no GPS, indoor, day/night, etc.) for un-interruptedsupport to ground personnel in the real-world; (C) safety andreliability: it will avoid people/structures and can be trusted to workevery time

The presently disclosed systems and methods address the navigation,guidance and control challenges by leveraging the collaborative and“following” nature of this application. The collaborative relationshipbetween the UAV and its user implies that the UAV has access to bothconfiguration and real-time information about the user. This data isleveraged in multi-sensor/multi-platform fusion algorithms that make oursystem robust to both aggressive relative motion and environmentaldisturbances.

The “following” relationship is in turn leveraged for intelligent pathplanning and obstacle avoidance. The key observation is that as theground user traverses the environment he naturally detects and avoidsobstacles, thereby defining an obstacle-free trajectory that can be usedby the UAV when it detects obstacles on its path. This greatlysimplifies the path planning task and removes the need for large-scaleenvironment sensing and map-building, which is one of the mostchallenging aspect to this problem for small UAVs.

According to one aspect, the present disclosure is directed to a methodfor navigating an airborne device relative to a target. The method maycomprise detecting, at an optical detector on the airborne device, anoptical signal generated by an LED on the target. The method alsocomprises comparing, by a processor on the airborne device, the detectedoptical signal with a previously-detected optical signal. The methodfurther comprises determining, by the processor based on the comparison,a change in location of at least one of the airborne device or thetarget. The method also comprises adjusting a position of the airbornedevice based on the determined change in location. The method alsocomprises predicting, by the processor, a movement of the target basedon information indicative of at least one of a position, an orientation,an acceleration, a velocity, or an altitude of the target, wherein theposition of the airborne device is adjusted based on the predictedmovement of the target.

In accordance with another aspect, the present disclosure is directed toa system for aerial monitoring of a target. The system comprises atarget device coupled to a target, wherein the target device comprisesat least one LED configured to generate an optical signal. The systemalso comprises an airborne device coupled to an airborne vehicle and indata communication with the target device. The airborne device comprisesan optical detector configured to detect the optical signal generated bythe target device, and a processor communicatively coupled to theoptical detector. The processor may be configured to compare thedetected optical signal with a previously-detected optical signal,determine a change in location of at least one of the airborne device orthe target, and generate a control signal for adjusting a position ofthe airborne device based, at least in part, on the determined change inlocation.

In accordance with another aspect, the present disclosure is directed toa method for aerial tracking of a target. The method may comprisedetecting, at an optical detector associated with the airborne device,an optical signal pattern generated by a plurality of LEDs associatedwith the target. The method may also comprise comparing, by a processorassociated with the airborne device, the detected pattern with apreviously-detected optical pattern and with a baseline pattern. Themethod may further comprise determining, by the processor based on thecomparison, a change in location of at least one of the airborne deviceor the target. The method may also comprise receiving, at the processorassociated with the airborne device from at least one sensor locatedon-board the target, information indicative of at least one of aposition, a rotation, an orientation, an acceleration, a velocity, or analtitude associated with the target. The method may also comprisepredicting, by the processor associated with the airborne device basedon the received information, a future movement of the target, andadjusting a position of the airborne device based, at least in part, onthe determined change in location and the predicted movement of thetarget.

According to certain exemplary embodiments, the presently disclosedsystems and methods provide a solution wherein the airborne devicefurther comprises a proximity/range sensor and the optical detectorincludes an image sensor associated with a digital camera. The airbornedevice may be configured to detect an obstacle in a flight pathassociated with the airborne device based on obstacle informationdetected by the proximity/range sensor and the optical detector, andadjusting a position of the airborne device is further based, at leastin part, on the obstacle information.

Alternatively or additionally to the above-described “machine vision”approach to obstacle detection/avoidance, the systems and methodsdescribed herein may leverage the collaborative (through bi-directionalcommunication) and “following” nature of this application. The keyobservation is that as the target traverses the environment, itnaturally detects and avoids obstacles, thereby defining anobstacle-free trajectory that can be leveraged by the UAV. When the UAVdetects obstacles ahead, it gets onto the user-defined (obstacle-free)path. It then closely follows behind the user until the obstaclesdisappear and it can safely return to its nominal perch position behindthe user. The processor associated with the airborne device 115incorporates this capability to detect obstacles and avoid them byfollowing the user-defined path until obstacles disappear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates one exemplary operation environment including a UAVand human user, in which the presently disclosed systems and methods foreffectively and accurately navigating an unmanned aerial vehiclerelative to a mobile target may be implemented, consistent with certaindisclosed embodiments;

FIG. 1B illustrates another exemplary operation environment including aUAV and human user, in which the presently disclosed systems and methodsfor effectively and accurately navigating an unmanned aerial vehiclerelative to a mobile target may be implemented, in accordance withcertain disclosed embodiments;

FIG. 1C illustrates yet another exemplary operation environmentincluding a UAV and human user, in which the presently disclosed systemsand methods for effectively and accurately navigating an unmanned aerialvehicle relative to a mobile target may be implemented, consistent withcertain disclosed embodiments

FIG. 2 illustrates an exemplary airborne device (AD), such as anunmanned aerial vehicle (UAV), in accordance with certain disclosedembodiments;

FIG. 3 illustrates an exemplary human user having at least one optionaltarget device, consistent with certain disclosed embodiments;

FIG. 4A provides a block diagram of exemplary components associated witha system for navigating an unmanned aerial vehicle relative to a mobiletarget, in accordance with certain disclosed embodiments;

FIG. 4B provides a block diagram of an exemplary components associatedwith an alternative system for navigating an unmanned aerial vehiclerelative to a mobile target, in accordance with certain disclosedembodiments;

FIG. 5 illustrates a schematic diagram of a system in which thepresently disclosed methods for navigating an unmanned aerial vehiclerelative to a mobile target, consistent with certain disclosedembodiments; and

FIG. 6 provides a flowchart depicting an exemplary process to beperformed by one or more processing devices associated with a system fornavigating an unmanned aerial vehicle relative to a mobile target, inaccordance with certain disclosed embodiments.

DETAILED DESCRIPTION

Systems and methods consistent with the disclosed embodiments aredirected to solutions for tracking of a target object (whether mobile orstationary) by an airborne device, such as an unmanned aerial vehicle(UAV). More particularly, the processes and features disclosed hereinprovide a solution for allowing the airborne device to accurately andreliably follow a target device, while maintaining a generally constantrelative distance from the target device and avoiding obstacles in thepath of the airborne device. Exemplary features associated with thepresently disclosed system include path prediction and collisionavoidance schemes for adjusting the flight path of the airborne deviceduring tracking of the target. One or more camera devices mounted on theairborne device are used for tracking of the target, as well asrecording video of the target for various uses, such as security;intelligence, surveillance, and reconnaissance (ISR) activities, aerialsearch and recovery, and recreational use, all autonomously, withoutrequiring specific user piloting activities.

FIGS. 1A-1C illustrate exemplary operational environments 100, 101, and102, respectively, in which the presently disclosed systems and methodsfor effectively and accurately navigating an unmanned aerial vehiclerelative to a mobile target may be implemented. As illustrated in eachof FIGS. 1A-1C, according to exemplary embodiments, the operationalenvironment 100, 101, 102 may include an airborne vehicle 110, such asan unmanned aerial vehicle (UAV) and one or more stationary or mobiletarget objects 120. In certain embodiments, airborne vehicle 110 may becommunicatively coupled via a data link 130 to one or more electroniccomponents or target devices (shown as reference number 150 of FIG. 1B)that may be mounted or otherwise coupled to target 120. As illustratedin FIG. 1 and as will be explained in greater detail in connection withthe figures and flowcharts that follow, airborne vehicle 110 may beconfigured to track target 120 from an aerial flight position 145 alonga flight path 140.

The presently disclosed system is designed to be integrate into existingUAVs in order to transform them into personal UAVs that are smarter andmore autonomous. As illustrated in FIG. 1B, the system generallycomprises two parts, an airborne device (AD) and a target or user device150. The AD (illustrated as reference numeral 115 of FIG. 2) is mountedon airborne vehicle 110 in a location that enables it to have anunobstructed view of target 120. The target device 150 is mounted on thetarget 120 and is connected to a set of LEDs (typically near-infrared(NIR), but other wavelengths of optical or thermal signals arecontemplated) distributed on the target 120.

In certain operational environments, the system may be configured withpath planning and obstacle detection/avoidance technology. Such anembodiment is illustrated in FIG. 1C. As illustrated in FIG. 1C and aswill be explained in greater detail below, the airborne vehicle may beequipped with proximity, machine vision, and image analysis hardware andsoftware that is configured to cooperate to monitor an optical pathway160 ahead of airborne vehicle 110 as the airborne vehicle follows target120 along flight path 140. Upon detection of an obstacle 147 in theoptical pathway, airborne device 115 may be configured to change theflight position 145 to define an alternate flight position 142 in orderto avoid obstacle 147.

In some situations, such a deviation may result in a temporary deviationof the general plan to maintain the relative range and trajectorybetween airborne vehicle 110 and target 120. As illustrated in FIG. 1C,for example, once airborne device 115 determines that the path aheadcontains obstacles, airborne device 115 may be configured to change theflight position 145 to redefine the flight position 142 to follow itsuser from directly behind, since the user defines an obstacle-free path.Once airborne device 115 determines that the optical patch 160 is clear,airborne device 115 may be configured to change the flight position 145to redefine the flight position 142 to restore the relative range andtrajectory between airborne vehicle 110 and target 120 to its defaultrelative navigation settings over flight path 140.

FIG. 2 illustrates a multi-rotor aerial vehicle 110 (e.g., a UAV), inaccordance with certain disclosed embodiments. As illustrated in FIG. 2,the UAV may comprise one or more electrical components adapted tocontrol various aspects of the operation of the UAV, which may bedisposed inside a housing or cavity associated with the airborne device110 or mounted to the airborne device 110, such as on the underside ofthe device. Such electrical components can include an energy source(e.g., battery), flight control or navigation module, GPS module (e.g.,GPS receivers or transceivers), inertial measurement unit (IMU) module,communication module (e.g., wireless transceiver), electronic speedcontrol (ESC) module adapted to control an actuator (e.g., electricmotor), actuator(s) such as an electric motor used to actuate a rotorblade or rotor wing of the UAV, electrical wirings and connectors, andthe like. In some embodiments, some of the electrical components may belocated on an integrated electrical unit such as a circuit board ormodule. One or more electrical units may be positioned inside thehousing of the airborne vehicle 110. When in use, the electricalcomponents discussed herein may cause interference (e.g.,electromagnetic interference) to other components (e.g., magnetometer)of the UAV. In some embodiments, the interference may be caused byferrous material or static sources of magnetism. For example, theelectrical components may comprise magnets that generate magneticfields, thereby causing magnetic interference.

As illustrated by FIG. 2, the body portion of the UAV comprises acentral housing member and one or more branch housing members. The innersurface of the central housing member can form a central cavity. Each ofthe branch housing members, in the shape of a hollow arm or any othersuitable shape, can form a branch cavity. When the central housingmember is connected to the one or more branch housing members, thecentral cavity and the one or more branch cavities can collectively formone unified cavity.

The branch housing members can be connected to the central housingmember in an “X” or star shaped arrangement. Specifically, the centralhousing member can be located at the center of the X or star shapedarrangement whereas the branch housing members can be distributed aroundthe central housing member, in a symmetric or asymmetric fashion. Insome embodiments, such a star-shaped arrangement can facilitateefficient electrical connection between electrical components disposedwithin the cavity of the housing, such as between a centrally locatedflight control module and the individual ESC modules located inrespective branch cavities. Or between a centrally located energy source(e.g., battery) and actuators (e.g., electric motors) used to drive therotors of a multi-rotor UAV. In other embodiments, the housing and/orthe cavity inside the housing of the UAV may have a shape other than thestar shape described herein. For example, the housing and/or the cavityinside the housing can form a substantially spherical, elliptical, orcylindrical shape or any other shape.

In a typical embodiment, the number of branch housing members is equalto the number of rotors or actuator assemblies of the UAV. An actuatorassembly (not shown) can include a rotor wing or rotor blade 112 a-112 dand an actuator that is used to actuate the rotor blade 112 a-112 d. Forexample, a four-rotor quadcopter such as illustrated in FIG. 2 may havefour branch housing members, each corresponding to one of the fourrotors or actuator assemblies. In the illustrated embodiment, the UAVhas four branches, each corresponding to one actuator assembly. That is,the UAV has four actuator assemblies. In various embodiments, the numberof the branches and/or the arrangement thereof may be different fromthose illustrated herein. For example, in some embodiments, there may bemore or less branch housing members and/or rotors or actuator assembliesthan illustrated here. For example, a 6-rotor UAV may have six rotors oractuator assemblies and six corresponding branch housing members. An8-rotor UAV may have eight rotors or actuator assemblies and eightcorresponding housing members. In alternative embodiments, the number ofbranch housing members may not correspond to the number of rotors oractuator assemblies of the UAV. For example, there may be more or lessbranch housing members than actuator assemblies. In various embodiments,the numbers of branches, actuator assemblies, and actuators can beadjusted according requirements of actual circumstances. To ensurestability of the UAV during operation, a typical multi-rotor UAV has noless than three rotors.

In various embodiments, the one or more electrical components may beadapted to control various aspects of the operation of the UAV. Suchelectrical components can include an energy source (e.g., battery),flight control or navigation module, GPS module (e.g., GPS receivers ortransceivers), inertial measurement unit (IMU) module, communicationmodule (e.g., wireless transceiver), electronic speed control (ESC)module adapted to control an actuator (e.g., electric motor), actuatorsuch as an electric motor that is used to actuate a rotor blade or rotorwing of the UAV, connecting members configured to electrically connectthe electrical components (such as electrical wirings and connectors),and the like. In various embodiments, some or all of the electricalcomponents of the UAV may be located inside the housing.

In some embodiments, some of the electrical components discussed abovemay be located on one or more circuit modules. Each circuit module caninclude one or more electrical components. For example, as shown inFIGS. 4A and 4B, the circuit module can include the main flight controlmodule that includes one or more processors (such as implemented by afield-programmable gate array (FPGA)) for controlling key operations ofthe UAV. As another example, the same or a different circuit module canalso include an IMU module for measuring the UAV's rotational rate, andacceleration. The IMU module can include one or more accelerometersand/or gyroscopes. As another example, the same or a different circuitmodule can also include a communication module for remotelycommunicating with a target device. For example, the communicationmodule can include a wireless (e.g., radio) transceiver.

The flight control module or processor is typically a key component or“brain” of an UAV. For example, the flight control module can beconfigured to estimate the current velocity, orientation and/or positionof the UAV based on data obtained from visual sensors (e.g., cameras),IMU, GPS receiver and/or other sensors, perform path planning, providecontrol signals to actuators to implement navigational control, and thelike. As another example, the flight control module can be configured toissue control signals to adjust the state of the UAV based on remotelyreceived control signals.

In some embodiments, the electrical components can include one or moreelectronic speed control (ESC) modules. An ESC module can be adapted tocontrol the operation of an actuator. The actuator can be part of anactuator assembly and configured to actuator a rotor blade or wing ofthe UAV. In some embodiments, the ESC module can be electricallyconnected to the flight control module on the one hand, and an actuatoron the other hand. The flight control module can provide control signalsfor the ESC module, which in turn provides actuator signals to theelectrically connected actuator so as to actuate the corresponding rotorblade. In some embodiments, feedback signals can also be provided by theactuator and/or the ESC module to the flight control module.

In some embodiments, the UAV also includes one or more connectingmembers for electrically coupling or connecting the various electricalcomponents of the UAV. Such connecting members can include electricalwires, cables, and the like that are used for transmitting power, dataor control signals between the components. For example, the connectingmembers can be used to electrically connect 1) an energy source and anactuator assembly; 2) a circuit module and an ESC module; 3) an ESCmodule and an actuator; 4) a communication module and a circuit module,or the like. In some embodiments, the connecting members have pluggableconnectors at the distal portions to facilitate plugging and unpluggingof the connecting members with respect to the electrical components.

In some embodiments, some or all of the electrical components discussedabove are pre-configured, pre-assembled or pre-connected by amanufacturer of the UAV. In such embodiments, no or very little userassembly and/or calibrate may be required for the UAV to operate, makingthe UAV “ready-to-fly” out-of-the-box. Such pre-configuration ofcomponents not only enhances the user experience by lowering thetechnical expertise required, but also reduces the errors or accidentscaused by user mis-configuration. In some embodiments, suchpre-configured or pre-assembled components can include the flightcontrol module, GPS receiver, ESC module, or any of the electricalcomponents discussed herein, or any combination thereof. In someembodiments, one or more electrical components may be pre-configured,pre-connected or pre-assembled as an electrical unit (e.g., a circuitmodule). The electrical unit may be necessary and sufficient forcontrolling operation of the UAV. In some embodiments, no additionaluser configuration is required for the pre-configured components tooperate properly out-of-the-box. In other embodiments, some amount ofuser configuration or assembly may be required. In other situations, theuser may define certain parameters, such as flight height and rangebetween the airborne vehicle 110 and target 120 from a plurality ofpre-selected parameters.

FIG. 3 illustrates an exemplary embodiment of a target device 120 thatmay be mounted or attached to a mobile target, such as a person. Theprimary external feature of the target device are the one or more LEDsused to generate optical signals or pulses that are detectable byairborne device 115 mounted on airborne vehicle 110. As illustrated inFIG. 3, LEDs may be arranged in a predetermined spatial pattern that,when compared to a previously-detected pattern and/or a defaultcalibration pattern, may be used, at least partially, in the estimationof the relative state vector by the airborne device in order todetermine the relative position, velocity, and orientation betweenairborne device 115 and target 120. As an alternative or in addition tospatial pattern, the one or more LEDs may be configured to flashaccording to a frequency or pattern that is either known a priori orcommunicated in real-time to the airborne device. This flashing patternmay be detected by one or more monochrome cameras located on-board theairborne device. A processor located on the airborne device may beconfigured to use the flash pattern to correlate images captured atdifferent times in order to robustly extract the location of the LEDs ineach image. The images captured at different times may be compensatedfor motion. The change in LED location from image to image may then beused, at least partially, in the estimation of the relative state vectorby the airborne device in order to determine the relative position,velocity, and orientation between airborne device 115 and target 120.

System Configuration

FIG. 4A illustrates an exemplary embodiment of sensor suite that is usedin the presently disclosed systems for effectively and accuratelynavigating an unmanned aerial vehicle relative to a mobile target. Asexplained, estimating the relative state is required so that theairborne vehicle 110 knows at all times where it is relative to thetarget 120 it intends to follow. This state is used in the flightcontrol laws that drive control actuators to ensure the airborne vehicle110 follows the prescribed path. Because the target 120 may have verydynamic motion, it is important that the entire relative state be usedfor control (not just relative position, but also relative velocity andacceleration). This is enabled by collaboration, with the target device150 sending its inertial information to the airborne device 115.

In order to make use of the information associated with the target 120,however, accurate knowledge of relative heading is required. If relativeheading is unknown, the acceleration measured by the target device 150cannot be related to airborne device 115 axes and the airborne device115 therefore cannot use it to provide key lead velocity andacceleration information to the control system. This would degrade theability of the airborne vehicle 110 to accurately track a giventrajectory. Accurate knowledge of relative heading enables the airbornevehicle 110 to follow the user under a much greater range of motion. Thesensor suite was therefore selected in order to maximize observabilityinto the entire relative state, whether or not GPS is present.

According to the embodiment illustrated in FIG. 4A, both the airbornedevice 115 and target device 150 have one or more inertial measurementunits (IMUs), static pressure sensors, tri-axial magnetometers, and/orGPS transceivers. Each of these one or more sensors—referred to hereinas the “core” sensors—are contained within respective sensor modules 416and 154 with are mounted on respective mounting plates 422 and 156 ofrespective airborne device 115 and target device 150.

According to one embodiment, the IMU may include or embody anyelectronic device that is configured to measure and report rotationalrates and accelerations. IMU may include a combination of accelerometersand gyroscopes. According to one embodiment, inertial measurementunit(s) may contain a 3-axis gyroscope, a 3-axis accelerometer, and a3-axis magnetometer. It is contemplated, however, that fewer of thesedevices with fewer axes can be used without departing from the scope ofthe present disclosure. For example, according to one embodiment,inertial measurement units may or may not include an on-boardmagnetometer. It may include only a 3-axis gyroscope and 3-axisaccelerometer, the gyroscope for calculating the orientation based onthe rate of rotation of the device, and the accelerometer for measuringearth's gravity and linear motion, the accelerometer providingcorrections to the rate of rotation information (based on errorsintroduced into the gyroscope because of device movements that are notrotational or errors due to biases and drifts). In other words, theaccelerometer may be used to correct the orientation informationcollected by the gyroscope. Similar the magnetometer can be utilized tomeasure the earth's magnetic field and can be utilized to furthercorrect gyroscope errors. Thus, while all three of gyroscope,accelerometer, and magnetometer may be used, orientation measurementsmay be obtained using as few as one of these devices. The use ofadditional devices increases the resolution and accuracy of theorientation information and, therefore, may be advantageous whenorientation accuracy is important.

Pressure sensor(s) may be a barometer or any other suitable device thatcan be used to determine changes in pressure, which, in turn, may beused to determine changes in altitude associated with the respectiveairborne device 115 or target device 150.

As illustrated in FIG. 4A, airborne device 115 may also include one ormore monochrome cameras 117, 419, each of which is configured to detectoptical signal emitted by LEDs 152 a-152 n associated with target device150. Airborne device 115 may also include one or more range sensors 418,420 configured to detect the range sensors that are configured to detectthe relative distance between the airborne device 115 and target device150. As illustrated in FIG. 4A, one set of camera and range sensor isdownward-facing and may be used to compute optical flow around theairborne device 115. The other set of camera and range sensor is mountedon a 3-D gimbal 421 and is used to track the LEDs 152 a-152 n associatedwith target device 150 and sense obstacles. Raw data from all sensors isprovided to the AD processing module, where it is fused to estimate therelative state, detect obstacle, and compute guidance commands that arethen sent to the autopilot (pitch, roll, yaw, thrust).

Airborne device 115 may be communicatively coupled to target device 150and may be configured to receive, process, and/or analyze data measuredby the target device 150. According to one embodiment, airborne device115 may be wirelessly coupled to target device 150 via respectivewireless communication transceiver(s) 417, 155 operating any suitableprotocol for supporting wireless (e.g., wireless USB, ZigBee, Bluetooth,Wi-Fi, etc.)

Wireless communication transceiver(s) 417, 155 associated with airbornedevice 115 and target device 150, respectively, may include any devicesuitable for supporting wireless communication between one or morecomponents of airborne device 115 and target device 150. As explainedabove, wireless communication transceiver(s) 417, 155 may be configuredfor operation according to any number of suitable protocols forsupporting wireless, such as, for example, wireless USB, ZigBee,Bluetooth, Wi-Fi, or any other suitable wireless communication protocolor standard. According to one embodiment, wireless communicationtransceiver 417, 155 may embody a standalone communication module,separate from the respective processing systems. As such, wirelesscommunication transceiver 417, 155 may be electrically coupled to therespective processing system of airborne device 115 or target device 150via USB or other data communication link and configured to deliver datareceived therein to the corresponding processing system for furtherprocessing/analysis. According to other embodiments, wirelesscommunication transceivers 417, 155 may embody an integrated wirelesstransceiver chipset, such as the Bluetooth, Wi-Fi, NFC, or 802.11xwireless chipset included as part of the respective processor ofairborne device 115 or target device 150.

Processing hardware 415, 153 associated with airborne device 115 andtarget device 150, respectively, may each include or embody any suitablemicroprocessor-based device configured to process and/or analyzeinformation collected by sensors associated with the respective system.According to one embodiment, processing system 415, 153 may each embodya general purpose computer programmed with software for receiving andprocessing, for example, position information associated with thecorresponding component of the system. According to other embodiments,processing hardware 415, 153 may be a special-purpose computer or ASICto perform specific processing tasks (e.g., ranging, path prediction,obstacle detection, or collision avoidance). Individual components of,and processes/methods performed by, processing hardware 415, 153 will bediscussed in more detail below in connection with the explanation of theoperational methods.

FIG. 4B illustrates a system configuration consistent with an alternateembodiment of the presently disclosed system for effectively andaccurately navigating an unmanned aerial vehicle relative to a mobiletarget. This alternative embodiment may be used to follow auser-designated target. In this system, the component setup for theairborne device 115 is substantially similar to that described in FIG.4A, and, therefore, will not be discussed in additional detail inconnection with FIG. 4B. The configuration of the target device 150differs in that, instead of LEDs, the target device 150 includes aplurality of lasers with range finding capabilities mounted on themounting plate 156. During operation, the user points the lasers at thetarget of interest, which transmits the data back to the airborne device115, which processes the data to determine the distance between the twoprojected points. The airborne device 115 uses the points and theirrelative spacing to infer range to the target. An IMU located on thetarget device provides information to predict the target motion andassist in tracking the laser spots.

Sensor Fusion

According to one embodiment, the only pre-processing performed on sensordata is on the images. Optical flow is extracted from thedownward-looking camera so that body-axis velocities can be measured.Images from the tracking camera are processed in order to reliablyextract the location of target device LEDs within the image.Furthermore, the collaborative nature facilitated by the bi-directionalcommunication between the airborne device 115 and target device 150makes this process robust to the various lighting conditions that thesystem will experience in the real-world.

According to one embodiment, the camera exposure setting may optimizedbased on the estimated distance and the known LED brightness, such that(1) motion blur is minimized while (2) disturbances from other sourcesin the NIR spectrum (sun, fire, glare, etc.) are minimized. Therobustness of LED extraction is further augmented by leveraging therelative state estimate and reduce the size of the image processing andLED search region of interest (ROI), consistent with the state estimateuncertainty.

The camera exposure is synchronized with the known flashing pattern ofthe LEDs, such that frames are captured in rapid succession with LEDs onand off. The relative state information is used to re-project pixelsfrom a set of images to a common time, such that images from the set canbe added and subtracted based on the respective known LED state. Thistime-correlation process will eliminate disturbance illumination not inphase with the LED flashing pattern, enabling the extraction of LEDlocation through blob detections.

According to one embodiment, the sensor data from both target device 150and airborne device 115 is then fused within an extended Kalman filter(EKF) to estimate the relative state vector.

The sensor suite is adapted to enhance observability into every statewhether or not GPS is present. States that are particularly challengingto estimate are relative distance and relative heading. Relativedistance is challenging because the range sensor will not always bepointed directly to the user, since it will also be used to scan forobstacles. Heading is always a challenging state to estimate, which isamplified by the fact that the magnetometer cannot be used due to thelarge disturbances in the magnetic field experienced indoors and closeto the ground. In this regard we note the following key features of ourapproach: Using multiple LEDs on the user enables camera updates toprovide observability into relative distance, velocity, relative pitch,roll, and heading, and all relative inertial biases (provided the LEDsspatial distribution is adequate).

When the relative bias between the airborne device 115 and target device150, static pressure sensors is estimated, these sensors provideobservability into relative distance as long as the airborne device 115is not at the same height as the target device 150 (range is intuitivelyobservable when relative height and elevation angle are known). Relativemotion of the airborne device 115 relative to the target device 150(vertical or horizontal) provides observability into relative distance.

When GPS is present on both airborne device 115 and target device 150,most states are observable through GPS and the camera. When GPS isabsent optical flow is necessary in order for the airborne device 115 X-and Y-axis accelerometer and gyro biases to be observable through bodyX- and Y-axis velocity updates. With these airborne device 115 biasesknown, the corresponding target device 150 biases are observed throughbearing updates to different LEDs.

As explained above, the presently disclosed system may be configured todetect obstacles and provide guidance to avoid them. To reliably addressthe obstacle detection and avoidance challenge our system leverages thecollaborative (through bi-directional communication) and “following”nature of this application. The key observation is that as the targettraverses the environment, it naturally detects and avoids obstacles,thereby defining an obstacle-free trajectory that can be leveraged bythe UAV. When the UAV detects obstacles ahead, it gets onto theuser-defined (obstacle-free) path. It then closely follows behind theuser until the obstacles disappear and it can safely return to itsnominal perch position behind the user. The processor associated withthe airborne device 115 incorporates this capability to detect obstaclesand avoid them by following the user-defined path until obstaclesdisappear.

As illustrated in FIG. 1C, the perception required to detect obstacleduring nominal flight can be constrained to a small volume of spacedriven by (1) vertically, the height difference between the airbornedevice 115 and target device 150; (2) laterally, a distance driven bysize of the airborne device 115 and its ability to track lateralposition; and (3) forward, a distance drive by the speed of the airbornedevice 115. A similar volume needs to be sensed in order to safelyreturn to the perch position. This is illustrated in FIG. 1C.

Using this volumetric calculation scheme, reliably addressing theobstacle avoidance task then only requires one ranging sensor withlimited range and scanning volume, something that can be accomplishedwith proximity and ranging sensors. According to one embodiment, thespeed of the airborne vehicle 110 may be limited by the speed of theuser, which will typically be under 5 m/sec for a dismounted user and 15m/sec for off-road vehicles. Allowing a minimum time-to-collision of 3sec requires obstacles to be detected up to about 60 m (allowing 1 secto scan the entire volume). Such range is achievable with small laserrangefinders available today (e.g., PulsedLight Inc. LIDAR-Lite). Bymounting this sensor on the pitch and yaw gimbal already hosting thecamera, the necessary volume can be efficiently scanned, while alsomeasuring the distance between airborne device 115 and target device150.

FIG. 5 illustrates a schematic diagram of a processing system in whichthe presently disclosed methods for navigating an unmanned aerialvehicle relative to a mobile target, consistent with certain disclosedembodiments. This processing system may be included as part of airbornedevice 115 or target device 150, and may include additional and/ordifferent computer components than those illustrated in FIG. 5. Forexample, database 505 and storage 504 may be omitted from the targetdevice 150 in order to reduce size, weight, and cost of the device.Essentially, FIG. 5 serves to illustrate the exemplary (and optional)hardware that may be used in performing the data processing and analysisthat is generally associated with the airborne device 115. It should beunderstood, however, that, given the collaborative nature of the system,some or all of these components may be included as part of target device150, as well.

As explained, the processing system associated with airborne device 115(and, optionally, target device 150) may be any processor-basedcomputing system that is configured to receive sensor information fromcore sensor package 416, calculate the relative position of one or moreof the airborne device 115 or target device 150, analyze the relativeposition information, and adjust the position of the airborne vehicle110 in order to track the target 120 and maintain a relative distancebetween the airborne vehicle 110 and target 120. Non-limiting examplesof such a processing system include a desktop or notebook computer, atablet device, a smartphone, wearable or handheld computers, ASIC, orany other suitable processor-based computing system.

For example, as illustrated in FIG. 5, processing system may include oneor more hardware and/or software components configured to executesoftware programs, such as range finding, collision avoidance, obstacledetection, path planning, just to name a few. According to oneembodiment, processing system may include one or more hardwarecomponents such as, for example, a central processing unit (CPU) ormicroprocessor 501, a random access memory (RAM) module 502, a read-onlymemory (ROM) module 503, a memory or data storage module 504, a database505, one or more input/output (I/O) devices 506, and an interface 507.Alternatively and/or additionally, processing system may include one ormore software media components such as, for example, a computer-readablemedium including computer-executable instructions for performing methodsconsistent with certain disclosed embodiments. It is contemplated thatone or more of the hardware components listed above may be implementedusing software. For example, storage 504 may include a softwarepartition associated with one or more other hardware components ofprocessing system. Processing system may include additional, fewer,and/or different components than those listed above. It is understoodthat the components listed above are exemplary only and not intended tobe limiting.

CPU 501 may include one or more processors, each configured to executeinstructions and process data to perform one or more functionsassociated with processing system 500. As illustrated in FIG. 5, CPU 501may be communicatively coupled to RAM 502, ROM 503, storage 504,database 505, I/O devices 506, and interface 507. CPU 501 may beconfigured to execute sequences of computer program instructions toperform various processes, which will be described in detail below. Thecomputer program instructions may be loaded into RAM 502 for executionby CPU 501.

RAM 502 and ROM 503 may each include one or more devices for storinginformation associated with an operation of processing system and/or CPU501. For example, ROM 503 may include a memory device configured toaccess and store information associated with processing system,including information for identifying, initializing, and monitoring theoperation of one or more components and subsystems of processing system.RAM 502 may include a memory device for storing data associated with oneor more operations of CPU 501. For example, ROM 503 may loadinstructions into RAM 502 for execution by CPU 501.

Storage 504 may include any type of mass storage device configured tostore information that CPU 501 may need to perform processes consistentwith the disclosed embodiments. For example, storage 504 may include oneor more magnetic and/or optical disk devices, such as hard drives,CD-ROMs, DVD-ROMs, or any other type of mass media device. Alternativelyor additionally, storage 504 may include flash memory mass media storageor other semiconductor-based storage medium.

Database 505 may include one or more software and/or hardware componentsthat cooperate to store, organize, sort, filter, and/or arrange dataused by processing system and/or CPU 501. For example, database 505 mayinclude historical data such as, for example, stored pattern LED patterndata that is used for relative state estimation. CPU 501 may alsoanalyze current and previous path parameters to identify trends inhistorical data. These trends may then be recorded and analyzed to allowthe airborne device 115 to more effectively navigate. It is contemplatedthat database 505 may store additional and/or different information thanthat listed above.

I/O devices 506 may include one or more components configured tocommunicate information with a user associated with system 300. Forexample, I/O devices may include a console with an integrated keyboardand mouse to allow a user to input parameters associated with processingsystem. I/O devices 506 may also include a display including a graphicaluser interface (GUI). In certain embodiments, the I/O devices may besuitably miniaturized and integrated with tool 310. I/O devices 506 mayalso include peripheral devices such as, for example, a printer forprinting information associated with processing system, auser-accessible disk drive (e.g., a USB port, a floppy, CD-ROM, orDVD-ROM drive, etc.) to allow a user to input data stored on a portablemedia device, a microphone, a speaker system, or any other suitable typeof interface device. According to one embodiment, I/O devices 506 may becommunicatively coupled to one or more monochrome cameras 117 and rangefinding devices in order to detect optical information transmitted byLEDs 152 a-152 d associated with target device 150.

Interface 507 may include one or more components configured to transmitand receive data via a communication network, such as the Internet, alocal area network, a workstation peer-to-peer network, a direct linknetwork, a wireless network, or any other suitable communicationplatform. For example, interface 507 may include one or more modulators,demodulators, multiplexers, demultiplexers, network communicationdevices, wireless devices, antennas, modems, and any other type ofdevice configured to enable data communication via a communicationnetwork. According to one embodiment, interface 507 may be coupled to orinclude wireless communication devices, such as a module or modulesconfigured to transmit information wirelessly using Wi-Fi or Bluetoothwireless protocols. Alternatively or additionally, interface 507 may beconfigured for coupling to one or more peripheral communication devices,such as wireless communication transceiver 417, 155.

Systems and methods consistent with the disclosed embodiments aredirected to solutions for tracking of a target object (whether mobile orstationary) by an airborne device, such as an unmanned aerial vehicle(UAV). More particularly, the processes and features disclosed hereinprovide a solution for allowing the airborne device to accurately andreliably follow a target device, while maintaining a generally constantrelative distance from the target device and avoiding obstacles in thepath of the airborne device. Exemplary features associated with thepresently disclosed system include path prediction and collisionavoidance schemes for adjusting the flight path of the airborne deviceduring tracking of the target. One or more camera devices mounted on theairborne device are used for tracking of the target, as well asrecording video of the target for various uses, such as security;intelligence, surveillance, and reconnaissance (ISR) activities, aerialsearch and recovery, and recreational use, all autonomously, withoutrequiring specific user piloting activities. FIG. 6 provides a flowchartdepicting an exemplary process to be performed by one or more processingdevices associated with a system for navigating an unmanned aerialvehicle relative to a mobile target, in accordance with certaindisclosed embodiments.

As illustrated in flowchart 600 of FIG. 6, the process may commence uponcapture of an image by the airborne device camera. This image may becorrelated with one or more of the previous images, with appropriatecompensation for motion between the various capture times. Thecorrelation process utilizes knowledge of the LEDs temporal pattern,such as flashing rate. The image correlation process results in theextraction of one or more LEDs associated with the target device.

The measured LED location(s) is then compared to the known spatialpattern of the LEDs on the target user. This information is used tocorrect the relative state estimate including position, velocity, andorientation. Additional sensor information from other sensors on theairborne device (IMU, Baro, Mag, GPS) is also used for this correction,if available. If sensor information is available from the target device(IMU, Baro, Mag, GPS), it is also use in the state correction.

The process may commence upon detection of at least one optical signalgenerated by an LED associated with a target device (Block 610). Forexample, an optical detector (such as a monochrome camera 117) of theairborne device 115 may detect at least one optical signal generated byan LED associated with the target device 150.

Upon detection of the optical signal, the received image data may becorrelated with previous images based on stored or received LEDinformation (temporal pattern) (Blocks 620, 622). The temporal patternmay have been configured by the user at the beginning of the use of thedevice, or it may be transmitted by the target device to the airbornedevice in real-time. Based on the correlation, the processor of theairborne device may extract LED locations in each image (Block 630).

The processor associated with the airborne device may correct relativestate estimate based on information contained from the target sensorsand airborne sensors and stored LED information (spatial pattern)(Blocks 640, 642, 644, 646). The spatial pattern may have beenpreviously detected by the airborne device 115, or may have beencalibrated by the user at the beginning of the use of the device.

Methods and processes disclosed herein may also include features forpredicting movement of target device based on collaboration between theairborne device 115 and target device 150 (Blocks 644, 646). Theseprocesses are predicated on the collaboration and sharing of informationbetween the airborne device processor and target device core sensors.Specifically, the airborne device processor may be configured to receiveinformation indicative of position, orientation, acceleration, velocity,or altitude of the target 120 relative to the airborne vehicle 110.Furthermore, based on the current and previously received informationindicative of position, orientation, acceleration, velocity, or altitudeof the target 120 relative to the airborne vehicle 110, the airbornedevice 115 may be configured to predict a movement or infer a futurepath associated with the target.

As an alternative or in addition to path planning that may be performed,airborne device may also be configured to detect obstacle in thepredicted path (Block 660). As explained, the perception required todetect obstacle during nominal flight can be constrained to a smallvolume of space driven by (1) vertically, the height difference betweenthe airborne device 115 and target device 150; (2) laterally, a distancedriven by size of the airborne device 115 and its ability to tracklateral position; and (3) forward, a distance drive by the speed of theairborne device 115. A similar volume needs to be sensed in order tosafely return to the perch position.

The position of the airborne device may then be adjusted to maintain thedesired relative position and/or distance between the airborne device115 and the target 150 (Block 660). As explained, processor 416associated with airborne device 115 may be configured to control a motoror actuator associated with the airborne vehicle 110 in order to makemodifications to the position of the airborne device relative to changesin the position of the airborne vehicle 110 and/or target 150 (Block670).

Using this volumetric calculation scheme, reliably addressing theobstacle avoidance task then only requires one ranging sensor withlimited range and scanning volume, something that can be accomplishedwith proximity and ranging sensors. According to one embodiment, thespeed of the airborne vehicle 110 may be limited by the speed of theuser, which will typically be under 5 m/sec for a dismounted user and 15m/sec for off-road vehicles. Allowing a minimum time-to-collision of 3sec requires obstacles to be detected up to about 60 m (allowing 1 secto scan the entire volume). Such range is achievable with small laserrangefinders available today (e.g., PulsedLight Inc. LIDAR-Lite). Bymounting this sensor on the pitch and yaw gimbal already hosting thecamera, the necessary volume can be efficiently scanned, while alsomeasuring the distance between airborne device 115 and target device150.

The target user naturally detects and avoids obstacles, so he defines anobstacle-free path that the UAV can follow when necessary. If the UAVdetects an obstacle along its current flight path, it will compute apath to connect it to the user-defined path, so it can follow in thefootsteps of the target user until the obstacles disappear.

Using this prediction and obstacle detection information, airbornedevice may be configured to control a motor or actuator associated withthe airborne vehicle 110 in order to make modifications to the positionof the airborne device relative to changes in the position of theairborne vehicle 110 and/or target 150 (Block 640).

While this specification contains many specific implementation details,these should not be construed as limitations on the claims. Certainfeatures that are described in this specification in the context ofseparate implementations may also be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation may also be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemsmay generally be integrated together in a single software product orpackaged into multiple software products.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed systems andmethods for effectively and accurately navigating an unmanned aerialvehicle relative to a mobile target. Other embodiments of the presentdisclosure will be apparent to those skilled in the art fromconsideration of the specification and practice of the presentdisclosure. It is intended that the specification and examples beconsidered as exemplary only, with a true scope of the presentdisclosure being indicated by the following claims and theirequivalents.

INDUSTRIAL APPLICABILITY

By integrating the presently disclosed relative navigation system intoan existing airborne devices, any small UAV can be transformed into apersonal UAV that autonomously assists individuals or vehicles inreal-time through its onboard payload. In addition to being downlinkedto a centralized ground control station, the video feed from the UAV canbe streamed directly to the individual or vehicle through a heads-updisplay (HUD), such as Google Glass. In certain scenarios the raw videofeed may need to be distilled into actionable data for the user, similarto military systems available today. It is contemplated that automatedvideo processing can be used extract features of interest (e.g. warmobjects) and may be used to automatically alert the user during theperformance of a mission (police patrol or pursuit, search-and-rescueoperation, etc.).

Furthermore, the collaborative relationship facilitated by thebi-directional communication between the airborne device that is mountedon the UAV and the target device mounted on the target ensures that theUAV has access to both configuration and real-time information about itsuser. This enables the presently disclosed system to be robust toaggressive relative motion and to environmental disturbances, making itideally suited to emergency responders and other applications involvinghighly-active, dynamic users (action sports, cinematography, military,etc.). For example, sensor data obtained by the airborne device from thetarget device may be used to (1) estimate relative velocity andacceleration (in addition to position) with high-accuracy andlow-latency, (2) increase robustness to rapid relative motion in thenavigation and machine vision algorithms, (3) provide robustness tovarying lighting conditions in the machine vision algorithms, and/or (4)coast through short-term line-of-sight occlusions between UAV and user.

By exploiting the collaborative and following nature of thisapplication, our system provides small UAVs with the accuracy andbandwidth necessary to tightly follow in the footsteps of its user while(1) being robust to aggressive relative motion and environmentaldisturbances and (2) avoiding obstacles. Key benefits of our approachcompared to current state-of-the-art methods include: (1) designed forhigh-dynamics applications with robustness to motion and estimation ofthe entire relative state (position, velocity, acceleration) atlow-latency; (2) fully addresses the obstacle avoidance challenge; (3)designed for the real-world with robustness to varying ambient lightingconditions, robustness to poor ambient magnetic environment (typical oflow-altitude or indoor flight), and avoidance of complex machine vision(no SLAM, feature extraction and tracking, etc.); (4) high-accuracy,high-bandwidth navigation information that allows for tight UAV flightcontrol laws; (5) high-availability of the navigation solution (GPS notrequired).

What is claimed is:
 1. A method for navigating an airborne devicerelative to a target, comprising: detecting, at an signal detectorassociated with the airborne device, at least one signal generated by asignal emitter associated with the target; correlating, by a processorassociated with the airborne device, the detected signal with apreviously-detected signal; determining, by the processor based on thecomparison, a change in location of at least one of the airborne deviceor the target; and adjusting a position of the airborne device based, atleast in part, on the determined change in location.
 2. The method ofclaim 1, wherein determining the change in location of the at least oneairborne device or the target includes calculating a range between theairborne device and the target.
 3. The method of claim 2, whereinadjusting the position of the airborne device includes adjusting theposition of the airborne device to maintain the range between theairborne device and the target to within a threshold range value.
 4. Themethod of claim 1, where relative motion of the airborne device relativeto the target device is used to estimate relative distance between thetarget and the airborne devices.
 5. The method of claim 1, furthercomprising receiving, at the processor associated with the airbornedevice from at least one sensor located on-board the target, informationindicative of at least one of a position, a rotation, an orientation, anacceleration, a velocity, or an altitude associated with the target. 6.The method of claim 5, further comprising: predicting, by the processorassociated with the airborne device based on the received information, amovement of the target; and wherein adjusting the position of theairborne device is further based, at least in part, on the predictedmovement of the target.
 7. The method of claim 5, wherein receivinginformation indicative of information indicative of at least one of aposition, an orientation, an acceleration, a velocity, or an altitudeassociated with the target includes receiving orientation informationfrom at least one orientation sensor located on-board the target.
 8. Themethod of claim 5, wherein receiving information indicative ofinformation indicative of at least one of a position, an orientation, anacceleration, a velocity, or an altitude associated with the targetincludes receiving acceleration and rotational information from at leastone inertial measurement unit located on-board the target.
 9. The methodof claim 5, wherein receiving information indicative of informationindicative of at least one of a position, an orientation, anacceleration, a velocity, or an altitude associated with the targetincludes receiving barometric pressure information from at least onebarometric sensor located on-board the target.
 10. The method of claim9, where a difference in static barometric pressure between target andairborne devices is used to estimate relative distance between thetarget device and the airborne device.
 11. The method of claim 5,wherein receiving information indicative of information indicative of atleast one of a position, an orientation, an acceleration, a velocity, oran altitude associated with the target includes receiving directionalinformation from at least magnetometer located on-board the target. 12.The method of claim 5, wherein receiving information indicative ofinformation indicative of at least one of a position, an orientation, anacceleration, a velocity, or an altitude associated with the targetincludes receiving GPS coordinates and velocities from at least one GPSmodule located on-board the target.
 13. The method of claim 1, whereinthe source emitter includes a plurality of LEDs, and wherein detectingat least one signal generated by a signal emitter associated with thetarget includes detecting a plurality of optical signals, each of theplurality of optical signals generated by a respective one of aplurality of LEDs located on-board the target.
 14. The method of claim13, wherein comparing the detected optical signal associated with apreviously-detected optical signal include comparing a pattern definedby the plurality of detected optical signals with a pattern associatedwith the previously-detected optical signal.
 15. The method of claim 14,wherein determining the change in location is based on the comparisonbetween the pattern defined by the plurality of detected optical signalswith the pattern associated with the previously-detected optical signal.16. The method of claim 13, wherein detecting at least one signal isperformed by an optical detector that includes an image sensorassociated with a digital camera, the method further comprisingtransmitting, by the processor associated with the airborne device, acontrol signal for adjusting at least one of an intensity, frequency, orflashing pattern of the LED device associated with the target.
 17. Themethod of claim 16, wherein the transmitting of the control signal foradjusting at least one of an intensity, frequency, or flashing patternof the LED device associated with the target is responsive to adetection of suspected ambient light sources by the image sensor thatare not associated with the target.
 18. The method of claim 16, whereinthe optical detector includes an image sensor associated with a digitalcamera, the method further comprising adjusting, by the processorassociated with the airborne device, an exposure of the digital camerabased on an intensity or flashing pattern of the at least one opticalsignal generated by the LED associated with the target.
 19. The methodof claim 13, wherein the plurality of LEDs are placed on the targetdevice, the method further comprising estimating one or more of relativedistance, relative velocity, a relative pitch, a relative roll, arelative heading, and relative inertial biases.
 20. The method of claim1, wherein the signal includes a signal comprising one or more of one ormore of a thermal signal, light in a visible wavelength, light in aninfrared (IR) wavelength, light in a near-IR wavelength, or light in anultraviolet (UV) wavelength.
 21. The system of claim 1, furthercomprising wherein the airborne device further comprises a proximitysensor and the optical detector includes an image sensor associated witha digital camera, wherein the method further comprises: detecting anobstacle in a flight path associated with the airborne device based onobstacle information detected by the proximity sensor and the opticaldetector; and wherein adjusting a position of the airborne device isfurther based, at least in part, on the obstacle information.
 22. Themethod of claim 21, wherein adjusting a position of the airborne deviceincludes adjusting, based on the detection of an obstacle, the positionof the airborne device to follow closely behind the target as it travelsalong an obstacle-free path, and wherein the position of the airborne isreturned to the flight path when the obstacle is no longer detected. 23.A system for aerial monitoring of a target, comprising: a target devicecoupled to a target, the target device comprising: at least one LEDconfigured to generate an optical signal; an airborne device coupled toan airborne vehicle and in data communication with the target device,the airborne device comprising: an optical detector configured to detectthe optical signal generated by the target device; and a processorcommunicatively coupled to the optical detector and configured to:compare the detected optical signal with a previously-detected opticalsignal; determine a change in location of at least one of the airbornedevice or the target; and generate a control signal for adjusting aposition of the airborne device based, at least in part, on thedetermined change in location.
 24. The system of claim 23, wherein theairborne vehicle further comprises at least one motor that iscommunicatively coupled to the processor of the airborne device andconfigured to operate in response to the control signal received by theprocessor.
 25. The system of claim 23, wherein the processor isconfigured to determine the change in location of the at least oneairborne device or the target includes calculating a range between theairborne device and the target.
 26. The system of claim 25, wherein theprocessor is configured to generate a control signal for adjusting aposition of the airborne device to maintain the range between theairborne device and the target to within a threshold range value. 27.The system of claim 23, wherein the target device further comprises atleast one sensor configured to measure information indicative of atleast one of a position, a rotation, an orientation, an acceleration, avelocity, or an altitude associated with the target.
 28. The system ofclaim 27, wherein the processor is further configured to: receive, fromthe target device, the information indicative of the at least one of aposition, an orientation, an acceleration, a velocity, or an altitudeassociated with the target; predict, based on the received information,a movement of the target; and wherein the control signal for adjustingthe position of the airborne device is further based, at least in part,on the predicted movement of the target.
 29. The system of claim 27,wherein the at least one sensor is an orientation sensor configured tomeasure information indicative of orientation information of the target.30. The system of claim 27, wherein the at least one sensor is aninertial measurement unit configured to measure acceleration androtational information of the target.
 31. The system of claim 27,wherein the at least one sensor is a barometric sensor configured tomeasure barometric pressure information of the target.
 32. The system ofclaim 27, wherein the at least one sensor includes at least onemagnetometer configured to measure directional information of thetarget.
 33. The system of claim 27, wherein the at least one sensorincludes a GPS module configured to measure GPS coordinates andvelocities of the target.
 34. The system of claim 23, wherein the atleast one LED includes a plurality of LEDs, each of which is configuredto generate a respective optical signal.
 35. The system of claim 23,wherein the optical detector is further configured to capture images inclose succession with one another based, at least in part, on the flashpattern of the at least one LED, and wherein the processor is furtherconfigured to compensate the images for motion that occurred betweensuccessive images, wherein the resulting images are compared to extractthe location of the LED(s) robustly, regardless of other disturbancelight present in one or more of the images.
 36. The system of claim 35,wherein the processor is configured to compare the detected opticalsignal associated with a previously-detected optical signal by comparingthe pattern defined by the plurality of detected optical signals with apattern associated with the previously-detected optical signal.
 37. Thesystem of claim 36, wherein the processor is configured to determine thechange in location based on the comparison between the pattern definedby the plurality of detected optical signals and the pattern associatedwith the previously-detected optical signal.
 38. The system of claim 23,wherein the optical detector includes an image sensor associated with adigital camera, wherein the processor is further configured to transmita control signal for adjusting at least one of an intensity, frequency,or flashing pattern of the LED device associated with the target. 39.The system of claim 38, wherein the transmitting of the control signalfor adjusting at least one of an intensity, frequency, or flashingpattern of the LED device associated with the target is responsive to adetection of suspected ambient light sources by the image sensor thatare not associated with the target.
 40. The system of claim 23, whereinthe optical detector includes an image sensor associated with a digitalcamera, wherein the processor is further configured to adjust anexposure of the digital camera based on an intensity or flashing patternof the at least one optical signal generated by the LED associated withthe target.
 41. The system of claim 23, wherein the optical signalincludes a signal comprising one or more of light that is in one or moreof a thermal signal, a visible wavelength, an infrared (IR) wavelength,a near-IR wavelength, or ultraviolet (UV) wavelength.
 42. The system ofclaim 23, wherein the airborne device further comprises a proximitysensor and the optical detector includes an image sensor associated witha digital camera, wherein the processor is further configured to: detectobstacles in a flight path associated with the airborne device based onobstacle information detected by the proximity sensor and the opticaldetector; and wherein the control signal for adjusting a position of theairborne device further based, at least in part, on the obstacleinformation.
 43. The system of claim 23, wherein the optical detectorincludes an image sensor associated with a digital camera, the methodfurther comprising transmitting, by the processor associated with theairborne device, a control signal for adjusting at least one of anintensity, frequency, or flashing pattern of the LED device associatedwith the target.
 44. The system of claim 43, wherein the transmitting ofthe control signal for at least one of an intensity, frequency, orflashing pattern of the LED device associated with the target isresponsive to a detection of suspected ambient light sources by theimage sensor that are not associated with the target.
 45. A method foraerial tracking of a target, comprising: detecting, at an opticaldetector associated with the airborne device, an optical signal patterngenerated by a plurality of LEDs associated with the target; comparing,by a processor associated with the airborne device, the detected patternwith a baseline pattern; determining, by the processor based on thecomparison, a change in location of at least one of the airborne deviceor the target; receiving, at the processor associated with the airbornedevice from at least one sensor located on-board the target, informationindicative of at least one of a position, a rotation, an orientation, anacceleration, a velocity, or an altitude associated with the target;predicting, by the processor associated with the airborne device basedon the received information, a future movement of the target; andadjusting a position of the airborne device based, at least in part, onthe determined change in location and the predicted movement of thetarget.
 46. The method of claim 45, wherein determining the change inlocation of the at least one airborne device or the target includescalculating a range between the airborne device and the target.
 47. Themethod of claim 45, wherein adjusting the position of the airbornedevice includes adjusting the position of the airborne device tomaintain the range between the airborne device and the target to withina threshold range value.
 48. The method of claim 45, wherein thebaseline pattern is a pattern detected at an initial calibration or apattern that was previously-detected by the processor.
 49. The method ofclaim 45, wherein receiving information indicative of informationindicative of at least one of a position, a rotation, an orientation, anacceleration, a velocity, or an altitude associated with the targetincludes receiving orientation information from at least one orientationsensor located on-board the target.
 50. The method of claim 45, whereinreceiving information indicative of information indicative of at leastone of a position, a rotation, an orientation, an acceleration, avelocity, or an altitude associated with the target includes receivingacceleration and rotational information from at least one inertialmeasurement unit located on-board the target.
 51. The method of claim45, wherein receiving information indicative of information indicativeof at least one of a position, a rotation, an orientation, anacceleration, a velocity, or an altitude associated with the targetincludes receiving barometric pressure information from at least onebarometric sensor located on-board the target.
 52. The method of claim45, wherein receiving information indicative of information indicativeof at least one of a position, a rotation, an orientation, anacceleration, a velocity, or an altitude associated with the targetincludes receiving directional information from at least magnetometerlocated on-board the target.
 53. The method of claim 45, whereinreceiving information indicative of information indicative of at leastone of a position, a rotation, an orientation, an acceleration, avelocity, or an altitude associated with the target includes receivingGPS coordinates and velocities from at least one GPS module locatedon-board the target.
 54. The method of claim 45, wherein the opticaldetector includes an image sensor associated with a digital camera, themethod further comprising transmitting, by the processor associated withthe airborne device, a control signal for adjusting at least one of anintensity, frequency, or flashing pattern of the LED device associatedwith the target.
 55. The method of claim 54, wherein the transmitting ofthe control signal for adjusting at least one of an intensity,frequency, or flashing pattern of the LED device associated with thetarget is responsive to a detection of suspected ambient light sourcesby the image sensor that are not associated with the target.
 56. Themethod of claim 45, wherein the optical detector includes an imagesensor associated with a digital camera, the method further comprisingadjusting, by the processor associated with the airborne device, anexposure of the digital camera based on an intensity or flashing patternof the at least one optical signal generated by the LED associated withthe target.
 57. The method of claim 45, wherein the optical signalincludes a signal comprising one or more of light that is in one or moreof a thermal signal, a visible wavelength, an infrared (IR) wavelength,a near-IR wavelength, or ultraviolet (UV) wavelength.
 58. The method ofclaim 57, further comprising wherein the airborne device furthercomprises a proximity sensor and the optical detector includes an imagesensor associated with a digital camera, wherein the method furthercomprises: detecting an obstacle in a flight path associated with theairborne device based on obstacle information detected by the proximitysensor and the optical detector; and wherein adjusting a position of theairborne device is further based, at least in part, on the obstacleinformation.